F.A. Costa Oliveira

Mechanical and thermal behaviour of cordierite–zirconia composites

Cordierite (Mg2Al4Si5O18) ceramics are susceptible of mechanical failure due to their low fracture toughness, which may hinder their application. Dispersion of ZrO2 in cordierite to improve the mechanical properties has been extensively studied. However, little is known about the effect of such additions on both the sinterability and the mechanical properties of cordierite bodies fabricated from talc, kaolin and alumina mixes with additions of monoclinic ZrO2, as most studies are concerned with additions of tetragonal ZrO2 to cordierite powders. The present paper describes the in situ fabrication, the thermal and mechanical properties of sintered cordierite-based ceramic matrix composites containing dispersed particles of ZrO2 obtained by mixing clay–talc–alumina mixtures with additions of monoclinic ZrO2 up to 40 wt.%. The results obtained clearly demonstrate that the thermal expansion coefficient (CTE), elastic moduli (E) and flexural strength (σr) were critically dependent on the mixing/milling conditions, the ZrO2 content and the retained porosity.

Newly developed cordierite–zircon composites

Abstract Cordierite-zircon ceramic composites were fabricated by die pressing a commercial cordierite powder with the addition of up to 10 wt-% zircon (ZrSiO4). Sintering of cordierite was enhanced by the ZrSiO4 addition through glass phase formation. With ZrSiO4 additions above 2·5 wt-% no further effect on the mechanical properties of the composites was observed. The maximum flexural strength at 2·5 wt-%ZrSiO4 addition was 84±7 MPa, about 30% higher than the 67±5 MPa found for pure cordierite. The strength of cordierite at 2·5 wt-%ZrSiO4 increased with sintering temperature up to 1300°C, owing to the enhanced densification. Above 1300°C, however, the strength was reduced as a result of the formation of large pockets of glassy phase. The average fracture toughness of cordierite was increased from 1·0 to 1·5 MPa m1/2 with the addition of ZrSiO . This toughening can be attri4 buted to crack deflection around ZrSiO4 particles rather than to residual compressive stresses imposed on the cordierite owing to thermal expansion mismatch between cordierite and the ZrSiO4 second phase.